CN111372850B - Flow fence for aircraft winglets - Google Patents
Flow fence for aircraft winglets Download PDFInfo
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- CN111372850B CN111372850B CN201880076006.3A CN201880076006A CN111372850B CN 111372850 B CN111372850 B CN 111372850B CN 201880076006 A CN201880076006 A CN 201880076006A CN 111372850 B CN111372850 B CN 111372850B
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- winglet
- leading edge
- tip
- flow fence
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C3/00—Wings
- B64C3/58—Wings provided with fences or spoilers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C23/00—Influencing air flow over aircraft surfaces, not otherwise provided for
- B64C23/06—Influencing air flow over aircraft surfaces, not otherwise provided for by generating vortices
- B64C23/065—Influencing air flow over aircraft surfaces, not otherwise provided for by generating vortices at the wing tips
- B64C23/069—Influencing air flow over aircraft surfaces, not otherwise provided for by generating vortices at the wing tips using one or more wing tip airfoil devices, e.g. winglets, splines, wing tip fences or raked wingtips
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T50/00—Aeronautics or air transport
- Y02T50/10—Drag reduction
Abstract
An aircraft wing is described herein that includes a wing leading edge, a wing trailing edge, and an airfoil defined by a wing upper surface and a wing lower surface. The wing extends from a root to a tip, and the tip has a tip chord. Winglets extend from the wing tip and have a winglet leading edge, a winglet trailing edge, a winglet inboard surface, a winglet outboard surface, a winglet root having a winglet root chord, and a winglet tip. A flow fence is disposed on the airfoil inboard of and overlapping the winglet. The flow fence is adapted to delay and/or prevent flow separation on the winglet inboard surface at high sideslip angles, thereby increasing lateral stability and linearizing aircraft behaviour at high sideslip angles.
Description
Background
Aircraft winglets are primarily intended to improve wing efficiency and thereby reduce the amount of induced drag due to wing lift. The winglet being canted up and out from the tip of the aircraft also generally contributes to positive lateral stability (i.e., the behavior of a fixed-wing aircraft flying at sideslip angles to roll with the tip facing up and down when leeward, which protects the aircraft roll orientation from disturbances).
Fixed wing aircraft in many cases fly at high angles of attack (i.e., the longitudinal attitude of the aircraft with respect to the oncoming airflow) and high sideslip angles (i.e., the directional orientation of the aircraft with respect to the oncoming airflow). At landing approach, fixed wing aircraft must fly at low speeds, which requires a higher angle of attack to maintain sufficient lift to continue flight. As the aircraft speed decreases during the leveling immediately before reaching the runway, the angle of attack required to maintain lift increases. Similarly, during a landing approach, crosswinds (i.e., winds oriented at an angle to the runway centerline) require the aircraft to fly at a sideslip angle, and both roll control inputs and yaw control inputs must remain aligned with the runway centerline during landing. As the crosswind value increases, or as the aircraft speed decreases relative to the crosswind speed, the sideslip angle required for straight line flight along the runway centerline increases.
Lateral stability is necessary for aircraft certification and flight safety. Lateral stability reduces pilot workload by tending to recover a wing horizontal attitude after a gust or other disturbance rolls the aircraft and in the event that the aircraft's roll flight control system (e.g., aileron) becomes inoperable during flight (i.e., due to disruption, cut by engine debris during an engine rotor burst event), the pilot still has to be able to use alternative ways to maneuver the aircraft, such as via the aircraft's yaw flight control system (e.g., rudder) and to reach sideslip angle. The U.S. code No. 14, item 23.177 of federal regulations (commonly referred to simply as "CFR"), places a requirement on the static lateral stability of aircraft.
At high sideslip angles and high angles of attack (i.e., when the winglet is in a high lift state), the airflow inside the winglet may separate from the surface. This separation effect reduces winglet lift, reduces lateral stability, and results in a change in roll moment behavior of the aircraft. The aircraft must meet certification requirements and reduce lateral stability. The accompanying change in roll moment behavior is also considered an undesirable or unsatisfactory lateral control characteristic of the aircraft, which may hamper the certification of the aircraft. This may be partially prevented by adding means to the winglet to prevent separation of the airflow; however, these devices may cause an increase in aerodynamic drag and aircraft weight, which may reduce aircraft performance even under flight conditions where they are not required (e.g., under cruise-like conditions with a slight angle of attack and a sideslip angle approaching zero). These devices also add to the cost of the aircraft and they may be considered aesthetically unappealing.
During normal operation, aircraft often fly through various atmospheric and meteorological conditions. At common flying altitudes (e.g., 45,000 feet above average sea level), the average ambient atmospheric temperature is between sea level conditions and-70°f. The ability of the fine water droplets suspended in clean atmosphere to exist in a supercooled state without any seed nuclei means that such moisture can exist as a suspension liquid at a temperature lower than typical freezing conditions. Intentional flight under conditions below freezing temperature in which supercooled liquid water droplets are suspended is referred to as "flight in a known ice formation region" (commonly abbreviated as "FIKI"). During flight in known ice regions, forward facing aircraft surfaces accumulate water as it flows through the water and seed water droplets nucleate. Without the anti-icing system, this water freezes into ice and thus accumulates on the aircraft surface. Fuselage icing generally reduces aircraft performance, stability, and controllability due to variations in the shape and texture of the aircraft surface. However, the previously discussed positive static lateral stability requirements still apply to aircraft, even during flight in known icing zones.
When an aircraft enters known ice formation flight conditions, ice contamination may accumulate on the forward facing surface (including the winglet leading edge) without the anti-icing system. Ice accumulation on the leading edge of the winglet helps the airflow separate from the surface above the winglet at lower, more common sideslip angles. This tendency to separate affects winglet lift and reduces lateral stability. Anti-icing systems are known that can heat the winglet leading edge to prevent ice build-up, or mechanically or chemically remove or prevent ice build-up. However, these anti-icing systems are often expensive, add significant weight, cost and complexity to the aircraft, require maintenance, and require additional aircraft safety systems (e.g., fault notification, leak detection of bleed air systems, etc.), and may result in the implementation of important aircraft system designs into existing aircraft designs.
More broadly, many types of leading edge surface contamination can reduce airflow around the winglet and produce the same effect as ice accumulation. Similar to the contamination of the flow surface by ice build-up, many other ground and flight conditions may also result in contamination of the leading edge surface with various media (e.g., dust, plant matter and other ground debris, ash, insects that are impacted in low-altitude flights, bird droppings, dry aircraft maintenance or working fluid residue, etc.).
One known device for improving stall characteristics of an aircraft by changing the airflow separation pattern on the main wing (not winglet) at high angles of attack is a wing stall fence. The wing stall fence is attached to the wing at a location further inboard of the wing tip. Another known device found on aircraft is a vortex generator that extends in front of and below the leading edge of the main wing and generates a vortex to improve the stall characteristics of the aircraft by varying the flow field above the leading edge of the main wing (not winglet) at high angles of attack. Neither the wing stall fence nor the vortex generator will contribute to increasing the lateral stability of the aircraft.
Finally, another known device on board an aircraft is a wingtip light barrier which is smaller and more forward of the winglet on the leading edge of the main wing and serves to block the direct of wingtip light into the pilot's eyes in the cockpit. The wingtip light barrier will not contribute to increased lateral stability.
Disclosure of Invention
According to one aspect, an aircraft wing includes a wing leading edge, a wing trailing edge, and an airfoil defined by a wing upper surface and a wing lower surface. The wing extends from a root to a tip, and the tip has a tip chord. Winglets extend from the wing tip and have a winglet leading edge, a winglet trailing edge, a winglet inboard surface, a winglet outboard surface, a winglet root having a winglet root chord, and a winglet tip. The flow fence is arranged on the airfoil surface inside the winglet and overlaps the winglet. The flow fence is adapted to delay and/or prevent flow separation on the winglet inboard surface at high sideslip angles, thereby increasing lateral stability and linearizing aircraft behavior at high sideslip angles.
According to yet another aspect, a method for preventing airflow separation on an inboard surface of a winglet extending from a wing tip of an aircraft wing at high sideslip angles is provided. The method comprises the following steps: positioning a flow fence on the upper side of the airfoil adjacent the winglet inner side surface; spacing the flow fence inward from the wing tip a distance of no more than 100% of the length of the root chord of the winglet; and extending the flow fence on the upper surface of the wing to a first position overlapping the winglet.
According to yet another aspect, an aircraft wing includes a wing leading edge, a wing trailing edge, and an airfoil defined by a wing upper surface and a wing lower surface. The wing extends from a root to a tip, and the tip has a tip chord. Winglets extend from the wing tip and have a winglet leading edge, a winglet trailing edge, a winglet inboard surface, a winglet outboard surface, a winglet root having a winglet root chord, and a winglet tip. The flow fence is arranged on the airfoil surface and on the inner side of the winglet. The flow fence extends from a first position on the upper surface of the wing overlapping the winglet to a second position on one of the upper surface and the lower surface of the wing. The inner side distance between the flow guide grid and the wing tip is not more than 100% of the length of the root chord of the winglet. The flow fence is adapted to delay and/or prevent flow separation on the winglet inboard surface at high sideslip angles, thereby increasing lateral stability and linearizing aircraft behavior at high sideslip angles.
Drawings
FIG. 1 is a top plan view of an aircraft including wings, each having an exemplary flow fence disposed on an airfoil inboard of a winglet.
Fig. 2 is an enlarged view of the left wing tip of the aircraft shown in fig. 1.
FIG. 3 is a partial side perspective view of the left wing tip shown in FIG. 1.
Fig. 4-11 are outboard side views of a left side wingtip according to the present disclosure, illustrating exemplary aspects of a flow fence.
Fig. 12 is a perspective view of the flow fence shown in fig. 6.
Fig. 13 is a top view (plan view) of the flow fence of fig. 12.
Fig. 14 is a rear view of the flow fence of fig. 12.
Fig. 15 and 16 are front views of the flow fence of fig. 12.
Fig. 17 depicts the positioning parameters of the flow fence along the transverse (spanwise) direction of the wing.
Fig. 18 shows the air flow over the left wing tip with and without the flow fence.
Fig. 19 shows the separation of the air flow on the tip inside surface of the winglet (represented by the black shaded area) with and without the flow fence at high sideslip angles.
Figure 20 shows the pressure coefficient on the winglet inner and outer surfaces at section A-A and the reduction of the winglet suction peak due to the flow fence (which corresponds to a reduction in airflow separation).
Figure 21 shows the pressure coefficient on the upper and lower surfaces of the wing at section B-B and the improvement in outboard wing airflow due to the flow fence.
Fig. 22 shows the aircraft roll moment coefficients and calculations for lateral stability and roll moment behavior at high sideslip angles with and without a flow fence.
Fig. 23 shows the aircraft roll moment coefficients and wind tunnel test results for a clean winglet without a flow fence, for an icing contaminated winglet without a flow fence, and for an icing contaminated winglet with a flow fence, with respect to lateral stability and roll moment behaviour at high sideslip angles.
FIG. 24 shows aircraft lift coefficients and wind tunnel test results for aircraft lift at high sideslip angles for clean winglets without a fence, for icing contaminated winglets without a fence, and for icing contaminated winglets with a fence.
Detailed Description
An aircraft wing is described herein that includes a wing leading edge, a wing trailing edge, a wing upper surface, and a wing lower surface. In one exemplary embodiment, a winglet extends from a wing tip and has a winglet leading edge, a winglet trailing edge, a winglet inboard surface, and a winglet outboard surface. A flow fence provided on the wing inboard of the wing tip extends to a position on the upper surface of the wing overlapping the winglet. When the winglet leading edge has contamination, including ice build-up, the lateral stability of the aircraft may be compromised or degraded due to airflow separation on the winglet inboard surface at high sideslip angles. The flow fence delays and/or prevents airflow separation on the winglet inboard surface at high sideslip angles, which increases lateral stability and linearizes aircraft behavior at high sideslip angles without adding complex devices (such as anti-icing systems), weight, and cost.
It should be understood, of course, that the description and drawings herein are merely exemplary and that various modifications and changes can be made to the structures disclosed without departing from the disclosure. The term "angle of attack" is the angle between the chord line of the wing of the depicted fixed-wing aircraft and the oncoming airflow or the opposing wind. It is well known that as the angle of attack of fixed wing aircraft increases, the separation of the airflow from the upper surface of the wing becomes more pronounced, which firstly reduces the rate of increase of the lift coefficient with increasing angle of attack and secondly limits the maximum lift coefficient achievable. The term "sideslip angle" is the angle between the aircraft centerline (e.g., the line separating the left and right halves of the aircraft when the aircraft is viewed in a top (planar) view) and the oncoming airflow.
Referring now to the drawings, in which like numerals refer to like parts throughout the several views, FIGS. 1-3 illustrate an aircraft 100 having a fuselage 102. The fuselage 102 may extend from a nose at the forward end 104 of the aircraft 100 to a tail 106 at the aft end 108 of the fuselage 102. The tail 106 may include one or more tail surfaces, such as vertical stabilizing wings 110 and/or horizontal stabilizing wings 112 for controlling the aircraft 100. The aircraft 100 may also include a pair of wings 120. In fig. 3, the aircraft 100 may be defined with reference to a coordinate system having a longitudinal axis X, a transverse axis Y, and a vertical axis Z. The longitudinal axis X may be defined as extending through the approximate center of the fuselage 102 between the forward end 104 and the aft end 108 (i.e., the aircraft centerline extends from the fuselage nose to the fuselage tail). The transverse axis Y may be oriented orthogonally relative to the longitudinal axis X and may extend generally outboard of the wing 120 relative to the center of the fuselage 102 (e.g., generally extending from one wing tip toward the other wing tip). The vertical axis Z may be oriented orthogonally relative to the longitudinal axis X and the transverse axis Y (i.e., generally from below the aircraft to above the aircraft).
Each wing 120 includes a wing leading edge 122 (the forward facing edge of the wing), a wing trailing edge 124 (the aft-most edge of the wing), and an airfoil defined by a wing upper surface 126 (typically a low pressure flow surface) and a wing lower surface 128 (typically a high pressure flow surface, see, e.g., fig. 4). And each wing 120 extends laterally from a root 130 (closest to the fuselage 102) to a tip 132 (furthest from the fuselage 102). One or more propulsion units 134 may be mounted to the wing 120 or the fuselage 102. Each wing 120 also includes a winglet 136, which may be substantially perpendicular (generally upward) relative to the wing tip 132.
In the exemplary embodiment, a flow fence 140 is disposed on wing 120, laterally inboard of wingtip 132 and winglet 136 (see FIG. 2). It should be noted that while winglets 136 and flow gates 140 of the present disclosure are described in the context of a fixed wing aircraft (such as the fuselage plus wing 100 shown in fig. 1), winglets 136 and flow gates 140 of the present disclosure may be applied to any aircraft of any configuration (e.g., any civilian aircraft, commercial or military aircraft, including wing-body hybrid aircraft, wing-body fusion aircraft, rotorcraft, horizontal or vertical stabilizers or other auxiliary lift surfaces) without limitation. It should also be appreciated that the air fence 140 may be used as an original equipment component for a new aircraft and to retrofit an existing fleet aircraft. Since the air fence 140 is directly coupled to the support structure of the wing 120, it can be easily installed on an existing aircraft.
Each winglet 136 includes a winglet leading edge 146, a winglet trailing edge 148, a winglet inner surface 150 (which is typically a low pressure flow surface), a winglet outer surface 152 (which is typically a high pressure flow surface), a wingletRoot 154 (which is located adjacent to wingtip 132) and winglet tip 156 (which is opposite the winglet root). The winglet root 154 is attached or otherwise coupled to the wing 120 at the wing tip 132. In the depicted aspect, winglet 136 is swept aft and may additionally be formed to have a winglet tip chord C wt With the root chord C of the winglet wl The winglet root chord is at the point where the winglet root 154 engages the wing tip 132 (see fig. 4). In the depicted embodiment, the intersection of winglet leading edge 146 with wing tip 132 is at wing tip 132 aft of wing leading edge 122. It is contemplated that the intersection of winglet leading edge 146 and wing tip 132 may be located approximately at wing leading edge 122. In the depicted embodiment, the winglet trailing edge 148 is located aft of the wing trailing edge 124. It is contemplated that winglet trailing edge 148 may engage or intersect tip 132 at any location not further aft than wing trailing edge 124 and may engage or intersect tip 132 at a location substantially at wing trailing edge 124. In the disclosed aspect, winglet 136 is configured such that winglet root chord C wl Specific wing tip chord C w Shorter and winglet root chord C wl Extends aft of the wing trailing edge 124.
Fig. 4-11 illustrate exemplary aspects of a flow fence 140 according to the present disclosure. In the depicted aspect of fig. 4, the flow fence 140 extends from a forward position on the wing upper surface 126 (aft of the wing leading edge 122) to a aft position overlapping the winglet 136 (between the winglet leading edge 146 and the wing trailing edge 124 and/or winglet trailing edge 148).
In the depicted aspect of fig. 5, the flow fence 140 extends from a forward position on the wing upper surface 126 (at the wing leading edge 122) to a rearward position overlapping the winglet 136 (between the winglet leading edge 146 and the wing trailing edge 124 and/or winglet trailing edge 148).
In the depicted aspect of fig. 6, the flow fence 140 extends from a location about the wing leading edge 122 between the wing leading edge 122 and the winglet leading edge 146 on the wing lower surface 128 to a location overlapping the winglet 136 between the winglet leading edge 146 and the wing trailing edge 124 and/or the winglet trailing edge 148 on the wing upper surface 126.
In the depicted aspect of fig. 7, the flow fence 140 extends from a location about the wing leading edge 122 between the winglet leading edge 146 and the wing trailing edge 124 and/or winglet trailing edge 148 on the wing lower surface 128 to a location overlapping the winglet 136 between the winglet leading edge 146 and the wing trailing edge 124 and/or winglet trailing edge 148 on the wing upper surface 126.
In the depicted aspect of fig. 8, the flow fence 140 extends around the entire wing 120 on both the wing upper surface 126 and the wing lower surface 128.
In the depicted aspect of fig. 9, the flow fence 140 extends around the entire wing 120 on both the wing upper surface 126 and the wing lower surface 128, and also extends aft of the wing trailing edge 124 and/or winglet trailing edge 148.
In the depicted aspect of fig. 10, the flow fence 140 includes a first flow fence portion 174 on the wing upper surface 126 and a separate second flow fence portion 176 on the wing lower surface 128. Each of the first and second flow fence portions 174, 176 extends from a location between the wing leading edge 122 and the winglet leading edge 146 to a location between the winglet leading edge 146 and the wing trailing edge 124 and/or the winglet trailing edge 148. The first flow fence member 174 overlaps the winglet 136.
In the depicted aspect of fig. 11, the flow fence 140 extends around the entire wing 120 on both the upper wing surface 126 and the lower wing surface 128, excluding the area of the wing leading edge 122 on both the upper wing surface 126 and the lower wing surface 128. More specifically, the flow fence 140 extends from a location on the upper surface 126 between the wing leading edge 122 and the winglet leading edge 146 about the wing trailing edge 124 to a location on the lower surface 128 between the wing leading edge 122 and the winglet leading edge 146.
Fig. 12 is a perspective view of the flow fence 140 shown in fig. 6. Fig. 13 is a top view of the flow fence 140 shown in fig. 6. Fig. 14 is a rear view of the flow fence 140 shown in fig. 6. Fig. 15 and 16 are front views of the flow fence 140 shown in fig. 6. The flow fence 140 (which is shaped to conform to the wing 120) includes a single or multi-piece body 160 that extends from a leading edge portion 162 to a trailing edge portion 164. Although shown as having a constant thickness T (see fig. 16), the body 160 of the flow fence 140 may have a varying thickness in the longitudinal direction (i.e., along the longitudinal axis X of fig. 3). For this particular illustrated embodiment, a mounting flange 166 integral with the body 160 extends generally perpendicularly from a mounting edge 168 of the body 160. The mounting flange 166 is provided with mounting apertures 170 and the mounting apertures receive fasteners (not shown) for attaching the flow fence 140 to the wing 120. The height H (see fig. 12) of the flow fence 140 is sized for a combination of considerations including, but not limited to: lateral stability is maintained under high sideslip with or without surface flow contamination; eliminating undesirable roll behavior at high sideslip angles; as well as the weight, cost, and aesthetics of the parts, while also limiting the impact of the height of the flow fence on the skin friction and induced drag associated with the wing 120. Further, the depicted aspect of the flow fence 140 has a C-shaped leading edge portion 162, with the mounting flange 166 following the shape of the leading edge portion 162. For this design, the mounting flange is mounted to both the upper wing surface 126 and the lower wing surface 128. However, it should be appreciated that the configuration of the mounting flange 166 may vary depending on the embodiment of the flow fence 140 described above.
The air fence 140 shown in fig. 12 is attached by means of a mounting flange 166; however, it should be understood that alternative ways for securing the flow fence 140 to the wing 120 are contemplated. By way of example, the flow fence 140 may be integrated directly into the wing 120 via a joint on the wing; the flow fence 140 may be integrally formed with the wing 120 to define an integral, one-piece design of the wing 120 and the flow fence 140; the flow fence 140 may be integrally formed with the winglet 136 to define an integral, one-piece design of the winglet 136 and the flow fence 140; the air fence 140 may be fastened, adhered or welded to the wing 120 through the use of attachment flanges on the mating side of the air fence 140; the flow fence may be fastened, adhered or welded to the wing 120 along the overlapping edges of the flow fence 140; and the flow fence 140 may be provided with an internal attachment flange that is secured to an internal wing or winglet structure.
Referring to FIG. 17, in a top view (plan view) of the wing 120, the air fence 140 is spaced from the inboard side of the wing tip 132 no more than the winglet root chord C wl 100% of the length of (c). According to one aspect, the air fence 140 is spaced no more than a small distance inboard of the wingtips 132Wing root chord C wl 60% of the length of (c). According to another aspect, the air fence 140 is spaced from the inboard side of the wing tip 132 no more than the winglet root chord C wl 30% of the length of (c).
As shown in fig. 18, the mounting flange 166 provides a secure attachment of the flow fence 140, wherein airflow flows from the wing lower surface 128 to the wing upper surface 126 and inwardly around the wing tip 132 and winglet leading edge 146 at high sideslip angles. The flow fence 140 is adapted to generate a vortex between the flow fence 140 and the winglet 136. Thus, the vortex redirects the airflow to limit low pressure peaks on the winglet leading edge 146, thereby delaying and/or reducing airflow separation on the winglet inner side surface 150 at high sideslip angles. It should also be appreciated that the flow fence 140 is adapted to create a positive pressurization. As is well known, increasing the sideslip angle of the winglet 136 produces a sharp low pressure peak. When the low pressure peak becomes too high, the negative airflow separates and over expands and the airflow no longer attaches to the winglet inside surface 150 (see fig. 19). The positive pressure from the airflow at the sideslip enters the inside and impacts the flow fence 140, which limits (or reduces) the low pressure peak and reduces the likelihood of airflow separation at the winglet inside surface 150 at high sideslip angles (see fig. 20). The vortex redirects the airflow back to the potential airflow separation direction to delay and prevent airflow separation.
Furthermore, with the positioning of the flow fence 140 relative to the wingtips 132 and winglets 136 as described above, the flow fence 140 is adapted to delay and/or prevent airflow separation on the winglet inner side surface 150 at high sideslip angles, thereby increasing lateral stability and linearizing aircraft behavior at high sideslip angles (see fig. 19-23). Furthermore, one aspect of the aircraft 100 is the lack of an anti-icing system for the winglet leading edge 146. After ice contamination on the winglet leading edge 146 during flight in the known ice bank (or similarly, after other flow surface contamination on the winglet leading edge 146 at times other than during flight in the known ice bank), the flow fence 140 is adapted to delay and/or reduce airflow separation on the winglet inboard surface 150 during sideslip conditions to further increase lateral stability after ice contamination or other contamination on the winglet leading edge 146. Thus, with respect to aircraft 100, airflow separation occurs at times other than icing at high sideslip angles. The flow fence 140 maintains the airflow and increases the sideslip angle at which airflow separation occurs beyond that required for aircraft type certification. In the event of ice build-up on the winglet leading edge 146, or possibly in the event of other flow surface contamination, airflow separation occurs at essentially any angle of attack, even at slight sideslip angles. The addition of the flow fence 140 reduces the amount of airflow separation and improves lateral controllability. It should be appreciated that the precise angle depends on the aircraft and may be different for alternative configurations of the aircraft.
Fig. 19 shows calculations that indicate that with the flow fence 140 attached to the airfoil, airflow separation (represented by the black shaded area) on the winglet inner side surface 150 may be delayed and/or prevented at high sideslip angles.
Fig. 20 shows the effect of the flow fence 140 on the pressure coefficient (derived from the calculation) at the winglet chord position at section A-A shown in fig. 20. Curve 200 is the pressure coefficient on the winglet inside surface 150 when the flow fence 140 is not included on the wing 120. Curve 201 is the pressure coefficient on the winglet inside surface 150 when the flow fence 140 is included on the wing 120. Curves 202 and 203 are corresponding pressure coefficient distributions on the wing outboard surface 152, regardless of whether the flow fence 140 is included on the wing 120 (i.e., the flow fence 140 does not substantially affect the pressure coefficient on the wing outboard surface 152). Curves 200 and 201 demonstrate that positive pressure from the airflow at sideslip enters the inboard side around the wing tip 132 and impacts the flow fence 140, which limits (or reduces) the low pressure peak on the winglet leading edge 146 and reduces the likelihood of airflow separation at the winglet inboard surface 150 at high sideslip angles. In the example of fig. 20, when the flow fence 140 is included on the wing 120, the low pressure peak on the winglet leading edge 146 is reduced by approximately 20%.
FIG. 21 illustrates the effect of the flow fence 140 on the pressure coefficient distribution at the chord position of the wing at section B-B depicted in FIG. 21. Curve 210 is the pressure coefficient distribution over the upper surface 126 of the wing at positive lift and with the inclusion of the flow fence 140 on the wing 120. Curve 211 is the pressure coefficient distribution on the upper surface 126 of the wing at positive lift and without the inclusion of the flow fence 140 on the wing 120. Curves 212 and 213 are corresponding pressure coefficient distributions on lower surface 128 of the wing, regardless of whether or not a flow fence 140 is included on wing 120 (i.e., flow fence 140 does not substantially affect the pressure coefficient on lower surface 128 of the wing). With the flow fence 140 attached to the airfoil, the pressure distribution around the wingtip 132 on the upper surface 126 of the wing changes and thus delays and prevents the separation of the airflow from the inboard surface 150 of the winglet. Furthermore, with the flow fence 140 attached to the airfoil, the airflow reattaches to the winglet 136, which increases the outboard wing lift.
FIG. 22 is a graph of aircraft roll moment coefficient with respect to aircraft sideslip angle without flow surface contamination (e.g., ice, etc.). Curve 220 is the aircraft roll moment coefficient relative to the aircraft sideslip angle when the flow fence 140 is included on the wing 120 of the aircraft 100. Curve 221 is an aircraft roll moment coefficient relative to aircraft sideslip angle when the flow fence 140 is not included on the wing 120 of the aircraft 100. The curves with these values of higher slope correspond to more positive lateral stability than the curves with lower slope. Furthermore, a substantially linear curve is equivalent to the desired controllability. Figure 22 shows that at high sideslip angles, the aircraft roll moment coefficient is higher when the aircraft includes a deflector grid 140. Further, the increased linearity of curve 220 compared to curve 221 shows a more desirable controllability. Line 222 is an improvement due to the flow fence 140.
Fig. 23 shows wind tunnel test results that demonstrate that lateral stability is generally linear to moderate sideslip angles during normal flight conditions (i.e., no flow surface contamination) and without the flow fence 140. Positive lateral stability may be compromised or degraded after contamination by the flow surface; however, with the air fence 140 attached to the airfoil, positive lateral stability (i.e., slope similar to that of normal flight conditions) may be maintained, which is an aircraft certification requirement. Fig. 24 shows wind tunnel test results that indicate that the aircraft lift associated with winglet 136 may be reduced after contamination by a flow surface and that the wing recovers a significant amount of lift lost due to contamination of the flow surface with the attachment of a flow fence 140.
The present invention also provides a method for preventing airflow separation on the winglet inboard surface 150 at high sideslip angles. The method generally includes positioning a flow fence 140 on the upper surface 126 of the wing adjacent the winglet 136; in a top plan view of the wing 120, the flow fence 140 is spaced inwardly from the wing tip 132 no more than the winglet root chord C wl A distance of 100% of the length of (see fig. 4); and extending the flow fence 140 on the upper surface 126 of the wing to a first position overlapping the winglet 136. The method further includes positioning the first position of the flow fence 140 between the winglet leading edge 146 and the wing trailing edge 124 and/or the winglet trailing edge 148. The method further includes extending the flow fence 140 on the upper surface 126 of the wing to a second position generally at the wing leading edge 122 or aft of the wing leading edge 122. Alternatively, the method further includes wrapping the flow fence 140 around the wing leading edge 122 to a second location on the wing lower surface 128 of the wing 120, and positioning the second location of the flow fence 140 on the wing lower surface 128 between the wing leading edge 122 and the wing trailing edge 124 and/or winglet trailing edge 148.
It will be appreciated that the above-disclosed features and functions, as well as other features and functions, or alternatives or variations thereof, may be desirably combined into many other different systems or applications. Further, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
Claims (9)
1. A wing of an aircraft, the wing comprising:
a wing leading edge, a wing trailing edge, and an airfoil defined by a wing upper surface and a wing lower surface, the wing extending from a root to a tip having a tip chord;
winglets extending from the wing tip and having a winglet leading edge aft of the wing leading edge, a winglet trailing edge, a winglet inboard surface, a winglet outboard surface, a winglet root having a winglet root chord, and a winglet tip; and
a flow fence, which is arranged on the airfoil inside the winglet in a top plan view of the wing, which overlaps the winglet in an outside side view of the wing, wherein in the outside side view of the wing the flow fence extends from a first position around the wing leading edge between the wing leading edge and the winglet leading edge on the lower surface of the wing to a second position between the winglet leading edge and the wing trailing edge and/or the winglet trailing edge on the upper surface of the wing,
wherein the flow fence is adapted to generate a vortex between the flow fence and the winglet by flowing an airflow around the wing tip and the wing leading edge from the lower surface of the wing to the upper surface of the wing, wherein the vortex redirects the airflow to limit low pressure peaks on the winglet leading edge,
wherein the flow fence is adapted to delay and/or prevent airflow separation on the winglet inside surface at high sideslip angles, thereby increasing lateral stability and linearizing aircraft behaviour at high sideslip angles.
2. The wing of claim 1, wherein the flow fence is adapted to redirect airflow moving up and inwardly along the upper surface of the wing back into an outward and upward direction along the inboard surface of the winglet.
3. The wing of claim 1, wherein the winglet leading edge lacks an anti-icing system and the flow fence is adapted to delay and/or reduce airflow separation on the winglet inboard surface in sideslip conditions after ice contamination on the winglet leading edge, thereby further increasing lateral stability in the event of contamination of the winglet leading edge surface.
4. The wing of claim 1, wherein in the top plan view of the wing, the deflector grid is no more than 100% of the length of the winglet root chord from the inboard spacing of the wing tip.
5. The wing of claim 4, wherein the inboard spacing of the deflector grid from the wing tip is no more than 60% of the length of the winglet root chord.
6. A method for preventing airflow separation at high sideslip angles on an inboard surface of a winglet extending from a wing tip of an aircraft wing, the method comprising:
positioning a flow fence on an upper surface of the wing;
spacing the flow fence inward from the wing tip a distance of no more than 100% of the length of the root chord of the winglet; and
generating a vortex between the flow fence and the winglet by flowing an airflow from the lower surface of the wing to the upper surface of the wing around the wing tip and the wing leading edge by extending the flow fence on the upper surface of the wing to a first position overlapping the winglet and wrapping the flow fence around the wing leading edge to a second position on the lower surface of the wing, wherein the vortex redirects the airflow to limit low pressure peaks on the winglet leading edge.
7. The method of claim 6, wherein the winglet leading edge is aft of a wing leading edge, and further comprising positioning the first position of the flow fence between the winglet leading edge and the wing trailing edge and/or the winglet trailing edge.
8. The method of claim 6, further comprising positioning the second location of the flow fence on the lower surface of the wing between the wing leading edge and the wing trailing edge and/or the winglet trailing edge.
9. A wing of an aircraft, the wing comprising:
a wing leading edge, a wing trailing edge, and an airfoil defined by a wing upper surface and a wing lower surface, the wing extending from a root to a tip having a tip chord;
winglets extending from the wing tip and having a winglet leading edge aft of the wing leading edge, a winglet trailing edge, a winglet inboard surface, a winglet outboard surface, a winglet root having a winglet root chord, and a winglet tip; and
a deflector gate disposed inboard of the winglet on the airfoil in a top plan view of the wing, wherein in an outboard side view of the wing the deflector gate extends from a first position on an upper surface of the wing overlapping the winglet to a second position on a lower surface of the wing, wherein in the top plan view of the wing the deflector gate is spaced inboard of the wing tip by no more than 100% of the length of the winglet root chord,
wherein the flow fence is adapted to delay and/or prevent flow separation at high sideslip angles on the winglet inner side surface, thereby increasing lateral stability and linearizing aircraft behaviour at high sideslip angles,
wherein the flow fence is adapted to generate a vortex between the flow fence and the winglet by flowing an airflow around the wing tip and the wing leading edge from the wing lower surface to the wing upper surface, wherein the vortex redirects the airflow to limit low pressure peaks on the winglet leading edge.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US201762597560P | 2017-12-12 | 2017-12-12 | |
| US62/597,560 | 2017-12-12 | ||
| PCT/US2018/065243 WO2019118623A1 (en) | 2017-12-12 | 2018-12-12 | Flow fence for an aircraft winglet |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN111372850A CN111372850A (en) | 2020-07-03 |
| CN111372850B true CN111372850B (en) | 2024-02-23 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201880076006.3A Active CN111372850B (en) | 2017-12-12 | 2018-12-12 | Flow fence for aircraft winglets |
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| Country | Link |
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| EP (1) | EP3724067A4 (en) |
| CN (1) | CN111372850B (en) |
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| CN104192294B (en) * | 2014-01-02 | 2016-09-14 | 中国商用飞机有限责任公司北京民用飞机技术研究中心 | wing structure and aircraft |
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Also Published As
| Publication number | Publication date |
|---|---|
| CN111372850A (en) | 2020-07-03 |
| EP3724067A1 (en) | 2020-10-21 |
| EP3724067A4 (en) | 2021-09-01 |
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